The present invention relates generally to methods for separating fine coal particles from a mixture containing fine coal particles and a liquid, and more particularly to methods for separating fine coal particles which have previously been subjected to a preheating operation preparatory to the pipeline charging of coal particles into coke ovens.
In the pipeline charging of coal particles into coke ovens, the coal is subjected to a combined particulizing and preheating operation preparatory to conveying through a pipeline to a coke oven. It is desirable to separate the coal particles from the preheat gas upstream of the coke ovens. The separation of coal particles from preheat gas is normally performed with cyclone separators. The preheated coal particles include both relatively coarse and relatively fine coal particles, some of the latter being smaller than 325 mesh. Virtually all of the relatively coarse coal particles and most of the relatively fine coal particles descend through the bottom of the cyclone separators. The gas is removed through the top of these cyclone separators, and this off gas contains some of the relatively fine coal particles. It is desirable to recover these fine coal particles from the gas to utilize the fuel value of the coal and to avoid air pollution. These fine coal particles are separated from the preheat gas with a liquid at a wet scrubber followed by a second cyclone separating stage. The scrubber effluent recovered at the second cyclone separating stage contains a mixture of the precipitating liquid and the fine coal particles, and this effluent is introduced into a flotation cell to separate the fine coal particles from the scrubber liquid.
Problems arise in obtaining a satisfactory recovery of the fine coal particles at the flotation cell.